1. Field of the Invention
The invention relates to a laminate material or laminate workpiece comprising a functional layer which is disposed on a backing layer, in particular a friction bearing layer with the structure of a solid but fusible dispersion with a matrix and at least one component which is dispersed in the matrix and which at least in the solid condition is insoluble in the material of the matrix or is soluble only in an amount smaller than the amount present, or with the structure of a substantially fusible mixture, which can be used for tribological purposes and which fixedly combined in itself, of components which are not soluble in each other or which are soluble in each other only in an amount smaller than the amount present, possibly/partly in crystal-like form.
2. The Related Art
Composite friction bearings may be considered as laminate materials or laminate workpieces. The functional layer of such friction bearings comprises a dispersion alloy, in particular lead bronze or an aluminium/tin dispersion alloy or an aluminium/lead dispersion alloy, and is applied to a backing layer, primarily of steel, which forms the bearing shell. In that connection, composite bearings of steel/lead bronze laminate material are of particular significance because of the high dynamic load-carrying capacity and the good run-in and emergency-running properties of the lead bronze. Due to the total insolubility of the two metals in each other in the solid condition, there is practically a mechanical mixture of copper and lead present in a functional layer consisting of lead bronze, and that mixture is produced from the homogeneous molten material in the course of a long setting time. The steel/lead bronze laminate materials which are conventionally used nowadays and which are produced by a strip coating process on steel are restricted to lead contents of up to about 22% by weight of the lead bronze. The difficulties in regard to manufacture of copper/lead alloys with lead contents within the miscibility gap, that is to say lead contents of between 40 and 50% by weight, are so great that hitherto such alloys have not been able to acquire any practical significance. Bonding between the steel backing member and cast lead bronze occurs through a strong metal bond between the steel backing member and the copper crystallites, the latter being formed primarily by solidification of the molten material. Therefore, formation of such copper crystallites must be encouraged. In practice, crystallites are achieved by holding the steel at a temperature of about 1100.degree. C. during casting of the lead bronze thereon. This procedure permits diffusion bonding between the steel and the copper crystallites. On the other hand, the structure of the lead bronze functional layer, which is heterogeneous due to the copper crystallites and lead precipitates gives rise to serious functional disadvantages in comparison with a homogeneous function layer structure. Comparable circumstances also arise in regard to friction bearing layers, representing the functional layer, consisting of aluminium/tin dispersion alloys and aluminium/lead dispersion alloys, as well as all conceivable functional layers for tribological purposes with a heterogeneous structure. For example, including the case of structures of mixtures which are fixedly combined in themselves and which are substantially fusible, of components which are not soluble in each other or which are soluble only in an amount which is smaller than the amount present.
German laid-open application (DE-OS) No. 29 37 108 already discloses a process for refining sliding alloys, in particular sliding or friction bearing alloys. Therein the alloy is subjected to a locally proceeding, punctiform melting effect by means of one or more highly concentrated energy or heat beams. The procedure is intended to cause sudden cooling of the molten material. The effect is achieved by progressive movement of the punctiform surface portion which is subjected to the energy or heat beam and by the dissipation of heat which occurs in the material of he functional layer. In that known process, the functional layer which has a heterogeneous material structure is melted in the punctiform areas over its entire thickness. However, the amount of heat which is supplied in that operation is so great that the intended sudden cooling effect is still so slow--not least having regard to the latent heat of fusion which is released again when the material re-solidfies--that that procedure results in formation of a heterogeneous structure which at best is somewhat refined in comparison with the original structure. It is not possible thereby to achieve a substantial improvement in the functional properties of friction bearing layers of dispersion alloys and other mixtures which can be used for tribological purposes. In the case of functional layers of lead bronze, there is also the consideration that the desired diffusion bonding effect is eliminated or at least made substantially worse because the functional layer is locally melted over its entire thickness.
It is also known from EP 130 175 A2 and 130 176 A2, in relation to friction bearings, to form areas of different levels of hardness in the running surface. These patents disclose a procedure which provides that delimited zones of the running surfaces are subjected to a heat treatment by a laser beam or an electron beam and are thus caused to start to melt or to undergo transformation due to melting. In that connection, however, the primary consideration is to provide for different levels of hardness by melting other alloys or other alloying constituents into the material.
Finally, it is known from German laid-open application (DE-OS) No. 36 36 641 and EP 212 938 A2 for sliding or friction bearing layers to be formed on a strip-like carrier, for example a steel backing member, by a procedure which provides that the alloying components are firstly applied in powder form to the backing member. The powder is then progressively locally melted, using a laser beam which is guided over the layer of powder in a predetermined pattern. Admittedly it is possible for the layers produced in that way from dispersion alloy to have a finer structure than that found in cast functional layers of dispersion alloy. However, it is also not possible in that way to produce functional properties which are comparable to those of a quasi homogeneous functional layer. In addition the fact that previously sprinkled powder is caused to melt progressively in a punctiform region means that the desired diffusion bonding between the backing layer and the functional layer cannot be attained.
In comparison therewith, the problem of the present invention is substantially to improve laminate material or laminate workpieces in such a way that on the one hand a securer bond--if possible from the point of view of the material involved, a diffusion bonding--is guaranteed between the backing layer and the functional layer, while at its surface which performs the function in question the functional layer is to have a structure which enjoys functional properties which are substantially improved in comparison with functional layers with a heterogeneous structure.